This invention relates to an improved hydraulically actuated "double acting" slip assembly, useful to intermittently grip well pipes and tubing and prevent axial movement while the pipe is being run into or pulled from a well through the slip assembly.
A double acting slip assembly of this type is a very useful part of well pipe handling machines and drilling and servicing equipment generally known as hydraulic workover or "snubbing" units, used to run and pull well pipes while maintaining pressure control of the well to prevent "blowouts" and "wild wells".
A double acting slip assembly, when actuated to grip pipe, will prevent internal well pressure from pushing the pipe up and out of the well or support the weight of pipe tending to fall into the well.
A double acting slip assembly is disclosed in U.S. Pat. No. 3,760,469 to Cicero C. Brown which utilizes slip segments moved radially to initially grip the pipe. The radial movement can be easily reversed while there is an axial pipe load on this slip assembly, resulting in inadvertent release of pipe to fall into or be blown from a well.
A double acting slip assembly structure is also disclosed in U.S. Pat. No. 4,269,277 to Benton F. Baugh, herein incorporated by reference. The Baugh structure includes friction plates which are pressed together by pipe movement, after gripping, to frictionally oppose rotation of a drive sleeve in a direction releasing the pipe. Both the Brown and Baugh devices may be power rotated to turn gripped pipe and use two or more hydraulic cylinders for operation.